Typically, engines today are designed to heat up quickly and run at higher operating temperatures than they used to in the recent past in order to reduce emissions and improve fuel economy. To achieve these objectives requires the use of less cooling water to maintain the cylinder bore walls at the desired operating temperature. This development has led to cylinder bore wall configurations in which only the upper portion of the cylinder bore walls are cooled with water rather than extending the full length of the cylinder bore. This is known as a shallow water jacket design. The terms "lower" and "upper," as used herein, refer to the relative relationship of objects to the engine crank axis. Objects which are closer to the crank axis than another particular object are said to be lower than this particular object.
The result of this development in current designs is that the upper portion of the cylinder bore walls is insulated by the water jacket which includes the outer cylinder block wall from ambient conditions within the engine compartment. This leaves the lower portion of the cylinder bore wall exposed at its outside surface to these outside engine ambient conditions. This further results in the reinforcement ribs and bosses for the attachment bolts being cast as extending directly from the cylinder bore wall below the shallow water jackets, which creates a non-uniform cylinder bore wall structure. This, in turn, leads to distortion of the cylinder bore walls due to the uneven stresses and temperatures that each cylinder bore wall now encounters, which can result in increased piston wear or require the use of larger than desired piston-to-bore clearances. In addition, the exposed lower cylinder bore walls lead to increased combustion noise emitted from the engine. Moreover, the shorter outer cylinder block wall reduces the overall stiffness of the engine block requiring additional cast reinforcement ribbing with increased overall weight of the engine block to maintain its overall structural stiffness.